In pulse tube cryocoolers of the Gifford-McMahon type, and other devices, rotary valves are used to control the flow of pressurized gas from a pressure source, such as a compressor, into the cryocooler. Rotary valves also control the flow of gas from the cryocooler back to the compressor. Valves of this sort are described in U.S. Pat. No. 3,205,668 to Gifford and U.S. Pat. No. 3,625,015 to Chellis. U.S. Pat. Nos. 5,335,505 and 5,412,952 to Ohtani et al. disclose Pulse Tube Refrigerators.
Rotary valves have a cylindrical piston which is rotatingly driven within a cylindrical sleeve. Multiple ports on both the piston and the sleeve register with one another at different points in the revolution of the piston. It is during this registration that pressurized gas is directed from one port to another, and therefore from a source to a predetermined destination.
During operation of a rotary valve in a pulse tube cryocooler of the Gifford-McMahon type, the valves rotate at about two revolutions per second. In order to properly seal the valve to prevent pressurized gas from flowing where it should not, the surfaces slide in relatively close proximity to one another causing substantial wear. Some conventional rotary valves have a rotating disc at one longitudinal end which is forced, by the high pressure gas, against the flat surface of the valve's housing. This disc seals the flow of gas, but due to the direct contact of the disc to the housing, substantial wear occurs. Typically, one of the two surfaces is made of a low friction material such as tetrafluoroethylene and the other is made of a hard material such as hardened steel. This type of seal typically wears out within one year of continuous operation.
The need exists for a rotary valve which requires less frequent replacement.